Feature Article - for release the week of  October 29, 2006

Dan Culbert - Extension Horticulture Agent

Gross Grubs for Halloween

It’s always fun to get scared for Halloween.  I have recently been bugged by several different larval insects that appear scary if you look close, and are kind of gross if you study their habits. 

While larva of Tortoise beetles may be occasional pests of Sweet potatoes, palms and some tropical trees, one is turning out to be a hero for a really scary weed, the Tropical Soda Apple.  Today’s column will introduce a few of these creepy chewing grubs that grow up to be beautiful beetles in our Florida Yards.

Trashy bugs

Several different kinds of insect larva have an unusual habit of collecting trash and carrying it around with them.  This trashy habit is thought to provide protection by camouflaging the insect under a pile waste material.

What makes the larva of the tortoise beetles especially gross is that they include their waste products in this collection of trash.  What kind of self respecting predatory creature would actually eat a pile of bug poop, right?  Pretty ingenious, those tortoise larva!

What makes them especially menacing is that these larva have a specialized structure called a fecal fork which is held above their body.  With this grotesque appendage, the whole slimy mess can cover the top of this insect.  Many of these grubs also have spines sticking out from their sides, which help to collect and hold more of this disgusting collection, adding to the effect.  If you dare, take a look at a few of the photos I’ve found showing these disgusting creatures.

Tortoise Beetle Larva are gross and scary looking creatures!
Golden Tortoise beetle larva, (Charidotella bicolor)  showing the trash on top of larva. Photo: Paul Choate, UF/IFAS	This diagram shows a typical Tortoise Beetle larva's "anal fork" which is attached to the back side of this insect.  It can hold  cast skins and fecal material to this structure and move it over the back of the body, forming a "shield" which deters predation. Drawing from FDACS/DPI	An especially menacing looking creature is a larval tortoise beetle found in Thailand. Photo by John Moore Chiang Mai
The Wild Olive Tortoise beetle is found in southern Texas.  The stripes, spikes and fork make this a scary looking creature, but it only consumes leaves of a particular Texas native tree. Photo: (c) Mike Quinn	A Scorpion-looking creature is the larva of a native Florida or Palmetto tortoise beetle Photo: J.F. Butler, UF/IFAS.	This Tortoise Beetle larva shows its fork extended backwards to expose the top of the insect. Photo (c) larvalbug

For such an ugly baby, the tortoise beetle turns out to be a real beauty.  Tortoise beetles may be of different sizes, but are generally about one-quarter inch long.  They may be marked with spots, stripes, speckles or crosses across their shiny backs, and can have a shiny metallic sheen that makes them quite attractive.

And if you look carefully, their bodies are also covered with a clear rounded shell.  It is thought that this smooth “tortoise shell” covering allows the beetles to hunker down on a leaf surface and ward off any predatory creature that would like to make a meal out of a tortoise beetle. 

For budding entomologists, take note: the brilliant shiny colors are seen only the live insects.  Photos are a good way to keep track of this brilliant coloration, as the pigments disappear when they die.  So don’t expect preserved or pinned collections of dead tortoise beetles to be as impressive as the creeping crawling tortoise beetles.

Sweet Potatoes and Gold Bugs

At last week’s State Master Gardener Conference, Hillsborough Horticulture Agent Sydney Park-Brown discussed some of her favorite landscape perennials.  She mentioned several of the ornamental Sweet Potato Vines such as “Margarita” and “Blackie”, but noted that sometimes the foliage can be riddled with many small holes.  She then introduced us to the Tortoise beetles.

One of the more common sweet potato pests found in this area is the Golden Tortoise Beetle. Also known as the Gold bug, (Charidotella bicolor) this insect eats all kinds of morning glory leaves, including both the ornamental and vegetable types.  The damage comes from both the adult beetle and the disgusting larva, and the holes in the leaves look a little like flea beetle damage.

Another non-native tortoise beetle (Chelymorpha cribraria) was found a few years ago in Fort Lauderdale and points south to the Keys.  It too enjoys only the taste of sweet potato family plants.  It has various color forms, is usually is red or brown in color, sometimes has markings, but has a different colored thorax.  This exotic invader has been found not only on ornamental and garden sweet potatoes but is an issue with some of our native endangered morning glory relatives.

Palms and Geigers

UF IFAS entomologists report a couple of other tortoise beetles that are sometimes seen on other groups of plants. Doug Caldwell has studied the Geiger Tree Tortoise beetle (Physonota calochroma floridensis), a very attractive creature that can skeletonize the leaves of the tropical Geiger Tree.  This attractive native ornamental has year round orange flowers, and if the beetles don’t slow it down, the occasional freeze in our area makes this a difficult landscape choice for Florida Yards

Another Tortoise beetle seen is the Florida or Palmetto tortoise beetle, Hemisphaerota cyanea, a beautiful small beetle that is found on a variety of native and exotic palms. It is our only tortoise beetle that feeds on palms.

TSA Leaf Beetle

One of the horrors of our local landscapes, pastures and roadsides is the exotic invasive weed, Tropical Soda Apple.  If you have not seen any of these large bushy plants that are covered with thorns on all parts of the stems and leaves, you probably don’t get out much.  Cattle eat the fruit and pass the seed on to wherever they do their business, spreading this wicked weed.

Scientists have discovered that another tortoise beetle and its larva will make a snack out of TSA. Years of research and testing have shown that the TSA leaf beetle (Gratiana boliviana) will only consume TSA, so damage to other related plants like tomatoes and potatoes is not expected.

According to Okeechobee Livestock Agent Pat Hogue, the early predictions of total control of TSA by this insect have not been realized.   However, anything that can reduce leaves is a useful tool in slowing down this plant from HE**.  In the near future, we expect this tortoise to slowly crawl all over South Florida and help keep TSA from spreading so rapidly.

I’ve placed more information on our Okeechobee web page, http://okeechobee.ifas.ufl.edu.  If you need additional information on Tortoise Beetles and their Larva, please email us at okeechobee@ifas.ufl.edu or call us at 863-763-6469.  Local residents can stop by our office at 458 Hwy 98 North in Okeechobee, and visit our Okeechobee County Master Gardeners from 1 to 3 PM on Tuesday afternoons.  Happy Halloween!

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Trade names, where used, are given for the purpose of providing specific information. They do not constitute an endorsement or guarantee of products named, nor does it imply criticism of products not named. The Florida Cooperative Extension Service - Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information, and other services to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin.  Florida Cooperative Extension Service / IFAS / University of Florida.  Larry A.  Arrington, Dean Last update: 10/27/2006 .  This page is maintained by Dan Culbert

Go to UF/IFAS webpage

References

Brown, Stephen. Cordia sebestena (Geiger Tree). Fort Myers : UF/IFAS Lee County Extension Service, 2006.  http://lee.ifas.ufl.edu/Horticulture%20Fact%20Sheets/CordiaSebestenaOrangeGeigerGeigerTree.pdf 

Capinera, John,  Golden tortoise beetle (Feature Creatures Article) EENY-14.  Gainesville: UF/IFAS Cooperative Extension Service, 2004.  http://creatures.ifas.ufl.edu/veg/potato/golden_tortoise_beetle.htm

Caldwell, Doug.  Geiger tree tortoise beetle. Naples: UF/IFAS Collier County Extension Service, undated. http://collier.ifas.ufl.edu/Horticulture/Geiger%20tortoise%20beetle.htm

ibid. Observations on some Insect Pests of Woody Ornamentals: Black Olive caterpillar, Geiger Tree Tortoise Beetle, and Cycad Aulacaspis Scale in Naples, Florida.  Lake Alfred: Proc. Florida State Horticultural Society, Vol. 118, pages 322-325. 2005.  Link to FSHS publication.

Gill, Stanton and Dutky, Ethel. Pest of Sweet Potato Vine? (TPM/IPM Report Weekly Report). Brookeville: Central Maryland Research and Education Center, UMD Cooperative Extension. May 29, 2004 http://www.agnr.umd.edu/ipmnet/04May28G.pdf 

Hall, Donald and Butler, Jerry F.  Palmetto tortoise beetle (Feature Creatures Article) EENY-232.  Gainesville: UF/IFAS Cooperative Extension Service, August 2001. http://creatures.ifas.ufl.edu/orn/palms/hemisphaerota_cyanea.htm 

Medal, J. C. , Cuda, J. P. and D. Gandolfo, D.  Biology of Gratiana boliviana, the First Biocontrol Agent Released to Control Tropical Soda Apple in the USA. ( ENY-826)  Gainesville: UF/IFAS Cooperative Extension Service, November 2003.  http://edis.ifas.ufl.edu/IN487 .

Thomas, Michael C. [Exotic] Tortoise beetle. (Feature Creatures Article) EENY-89. Gainesville: UF/IFAS Cooperative Extension Service, June 1999.  Originally published as DPI Entomology Circular No. 363, FDACS/DPI. http://creatures.ifas.ufl.edu/veg/potato/tortoise_beetle.htm